Actually, you get the desired effect if you set the speed to NEGATIVE 0.3:

<?php if($integral['hero-parallax-toggle']==1) { ?> $('#welcome').parallax("50%", -0.3); <?php } ?>
<?php if($integral['testi-parallax-toggle']==1) { ?> $('#testimonials').parallax("50%", -0.3); <?php } ?>
<?php if($integral['calltoaction-parallax-toggle']==1) { ?> $('#calltoaction').parallax("50%", -0.3); <?php } ?>
<?php if($integral['newsletter-parallax-toggle']==1) { ?> $('#newsletter').parallax("50%", -0.3); <?php } ?>